1. Technical Field
The present invention relates to the technical field of an onboard battery that is mounted in a vehicle such as an automobile and is provided with a battery module accommodated in an accommodation case.
2. Related Art
In various vehicles such as an automobile, an onboard battery for supplying electric power to a motor and various electrical components is mounted.
These days, vehicles such as, in particular, electric vehicle (EV), hybrid electric vehicle (HEV), and plug-in hybrid electric vehicle (PHEV) are becoming pervasive, and an onboard battery having a high power storage function is mounted on these vehicles that use electricity as power.
The onboard battery is provided with an accommodation case and a battery module accommodated in the accommodation case, and the battery module is configured by arranging a plurality of battery cells (secondary batteries) such as, e.g., nickel-metal hydride batteries and lithium ion batteries. In the onboard battery mounted in the electric vehicle or the like, in order to achieve a high capacity storage function, a plurality of the battery modules is disposed in the accommodation case, and the individual battery cells of the plurality of the battery modules are connected in series or in parallel.
The onboard battery described above includes, as a configuration in which the high power storage function is achieved, an onboard battery in which the battery modules are arranged in upper and lower tiers in the accommodation case (see, e.g., Japanese Patent No. 5206110).
The onboard battery described in Japanese Patent No. 5206110 is disposed in a trunk on the rear side, the battery module in the lower tier is inserted into a disposition depression that is formed in a floor panel so as to be opened upward, and large space is thereby secured in the trunk. The front surface on the side of the lower tier of the accommodation case that accommodates the battery module is formed as an inclined portion that is displaced forward in an upward direction. The lower tier of the onboard battery is positioned between side members (side frames) of a vehicle body.
In the onboard battery described in Japanese Patent No. 5206110, when a large load is applied to the onboard battery from the rear due to a collision of a vehicle, the inclined portion of the accommodation case is guided by a front surface forming the disposition depression, and the entire onboard battery is moved obliquely upward and forward so as to avoid a cross member positioned on the front side of the disposition depression. Consequently, the onboard battery does not collide with the cross member, and an excessive stress to the battery module accommodated in the accommodation case is suppressed.
However, in the onboard battery described in Japanese Patent No. 5206110, in the case where the large load is applied from the rear, the entire onboard battery is moved obliquely upward and forward irrespective of the position of the applied load in a vertical direction. At this point, the inclined portion is guided by the front surface forming the disposition depression. When the inclined portion is guided by the front surface, the inclined potion and the front surface forming the disposition depression come into contact with each other, and hence a reaction force (a component force in a horizontal direction) to the collision is applied to the onboard battery from the front surface.
Consequently, although the excessive stress to the battery module is suppressed by the movement of the onboard battery in the obliquely upward and forward direction, the stress may be applied to each of the battery module in the upper tier and the battery module in the lower tier that are accommodated in the accommodation case depending on the magnitude of the load (the magnitude of the reaction force).
Since the lower tier of the onboard battery is positioned between the side members, in the case where a vehicle such as a passenger car collides, the large load is less likely to be applied to the onboard battery. On the other hand, the position of the upper tier of the onboard battery corresponds to the position of a frame of a large vehicle such as a truck in the vertical direction. Thus, in the case where the large vehicle collides, the large load is applied to the onboard battery. In such case, with the large load, the stress is applied to each of the battery module in the upper tier and the battery module in the lower tier, and the possibility of occurrence of smoking or ignition resulting from damage to the battery module or the like is increased.